Ordered arrays of crystalline-Si (c-Si) microwires, fabricated by the chemical-vapor-deposition, vapor-liquid-solid (CVD-VLS) growth mechanism, were pioneered nearly five years ago for sunlight-to-electrical power conversion. The VLS method is a robust and scalable approach for growth of crystalline materials from gaseous precursors. Specifically, the ability to directly produce high-quality, single-crystalline semiconducting material, without the need for further purification or wafering, makes SiCl4 VLS growth an interesting approach for production of Si for energy-conversion applications.
The lab-scale processes developed to date to prepare the Si substrates required for the VLS growth of highly-ordered silicon microwire arrays rely on expensive, high-temperature and high-vacuum techniques. In previous work, an oxide-coated (111)-oriented Si growth wafer was photolithographically patterned to introduce a confining layer that prevents the catalyst droplets from aggregating during VLS growth, and controls the spacing and diameter of the resulting Si microwires. The VLS catalyst material (Cu, 99.999%) was then deposited across the entire wafer via thermal evaporation under high vacuum, and the excess metal was removed by lift-off in acetone. Demonstrating a more energy and cost efficient patterning technique would allow these microwire arrays to be manufactured in a high throughput manner and would be more broadly applicable to microstructured device manufacturing. Progress on this front has included demonstrating that the Si(111) substrate can be reused a limited number of times if the wires are peeled off in a flexible polymer film and catalyst metal is electrodeposited into the remaining oxide pattern.